Method and device for treating hydrophilic sludge by hydraulic turbulence effect combined with oxidation and chemical reactions by additive input

ABSTRACT

A method and device for treating sludge and slime to enable reuse in soil upgrading and in building material systems. Hydrophilic sludge and slime having a water content not less than 70% are continuously treated in a manner which enables colloid removal, dehydration, oxidation, sanitation, stabilization, mineralization, filtration and porosification. The device for treatment includes a hollow caisson traversed in the longitudinal direction by the treated product and provided with at least an intake for the product to be treated and at least an outlet for the treated product.

The present invention concerns a device for treating sludge and slime toenable reuse in soil upgrading and in building material systems.

The technical field of the invention is the manufacturing of equipmentfor treating sludge and slime.

These products are traditionally dehydrated by evaporation, bycentrifuging or by filtration so as to separate the solid fraction fromthe liquid fraction.

In the case of evaporation, the products are heated to extract theirliquid phase.

With filtration, the liquid and solid phases are separated. Filtrationis the most widely used method of treating. These techniques are vacuumfiltration, pressurised filtration in chambers sealed by filters,chamber plate presses, membrane plate or automatic presses, or evenpressure strip filters, friction presses or centrifugal presses.

When they are put into practice these techniques have a fairly low yielddue to the fact of the physical characteristic of water in the productsto be treated. Water is in two forms, free or trapped in the solidstructure. The yield from these devices is often improved by theaddition of flocculant or coagulant additives.

The effectiveness of these techniques of evaporation and filtration islimited due to the texture of the treated products. Sludge and slime areproducts with liquid and solid phases, which are difficult to bedissociated because of the presence of colloidal material. Molecules ofa very small size constitute these materials, less than one tenth of amicron, very difficult to decant in water and collecting in hydrophilicpackets within the fraction solid. By means of this water retentioneffect, these materials prevent efficacious dehydration of the sludgeand slime which thus remain very humid, heavy, non-porous products, withdelicate upgrading especially in the agricultural field.

The object of the method according to the present invention is to remedythe problem of separation in sludge and slime thanks to a strong actionon the colloidal material. Originating from in-depth studies on thetexture of this material and from putting into perspective of theupgrading potential of these products, the method described hereincomprises series of mechanical shocks, oxidation and chemical reactionscarried out continuously within specific equipment.

The sludge and slime treated by this equipment are strongly hydrated andfluid, comprising at least 70% of water. The remainder comprises solidmineral and organic materials whereof one part is the colloidalmaterial. The mechanical shocks, the oxidation and the chemicalreactions act especially directly on the colloidal material by breakingit and by causing it to react with a reagent in order to modify its formand to extract structural water from it. This material, hydrophilic atthe outset rejoins the rest of the solid hydrophobic fraction, thanks totreatment thus facilitating dissociation of the two liquid and solidphases.

The treated products are organic hydrophilic products with a rate oforganic matter often greater than 40% of the total of the dry material,such as sludge from purification stations and effluent from thefood-processing industry, breweries, slaughterhouses, dairies,canneries, breeding, but also hydrophilic mineral products, whereof theorganic matter content can also exceed 40%, such as dredging slime fromrivers, canals, ponds, lakes, retaining basins, harbours, or evenfibrous sludge from the papermaking industry.

The following description referring to the attached diagrams and givenby way of non-limiting example illustrates one of the preferredembodiments of the invention.

FIG. 1 is a drawing of equipment for applying the method;

FIG. 2 is a cutaway view of the equipment illustrated in FIG. 1, in atransverse direction along line A-A.

The equipment is a caisson parallelepiped in shape, divided into hollowcompartments 6 separated by walls allowing transfer 9 of material fromone compartment to the other and also provided at least on one of theirfaces with elastic means 7 capable of causing strong turbulence bycounter-currents inside each compartment.

Each hollow compartment is open to the exterior by means of at least onecircular opening 2 and 3 for connecting to a compressor, a pump or othersimilar equipment. The caisson is elongated in shape. The end sectionsare provided with inlet devices 1 for products to be treated and outletdevices 4 for treated products.

In its lower part, the equipment is fitted with a filtration means forevacuating part of the liquid phase during its course in the caisson.Filtration is carried out by a textile structure 8 occupying the surfaceof at least one compartment. Evacuation is carried out by gravity underthe equipment. Depending on the treated products, this gravityevacuation 5 is open or closed to runoff. The equipment is made ofstainless steel, allowing to benefit from the catalytic action of Fe³⁺ions. The equipment works without limiting flow rate by adapting itsdimensions. It is constituted for example by a hollow caissonparallelepiped in shape, characterised by a small-surface sectiontransverse to the flow and a considerable length parallel to the flow ofat least 3 times the length of the longest side of the sectiontransverse to the flow.

The method comprises two phases: one phase in which mechanical shocksand oxidation of the material are caused, and one phase in whichchemical reactions are triggered by the addition of additives. The twophases are consecutive. The method functions continuously withoutretaining phase.

The products to be treated are introduced into the equipment at one ofits ends. They undergo a phase of strong turbulence caused by theintroduction of pressurised air and further by the presence of elasticmeans secured to the walls (or integrated into the walls) of thecompartments making up the equipment. Walls positioned perpendicularlyto the flow define these hollow compartments. These walls, which ensurethe flow of the products, are also holed and fitted with elastic meanscausing opposite currents of material and consequently the desiredshocks. The counter-currents cause shocks to the constituents of thematerial, thus breaking the colloidal mass and performingauto-filtration of the product between its different fractions inducingscreening between liquid and solid fractions. These effects thusfacilitate separation of the two solid and liquid phases. The forced andturbulent aeration contributes strong oxidation of the material. Theeffect of the aeration of the products is to destroy the anaerobicmicroorganisms, which might have formed into the products.

The product passes from one compartment to the other by losing power andwater.

The water passes over a filtering textile structure situated at thebottom of each compartment. These filtering structures communicate toallow the water to drain out via an orifice located at the bottom of theequipment. The product continues on its way, in the equipment, agitatedby turbulence and pressure becoming weaker and weaker. Liquid or solidadditives are introduced, benefiting from a relative fall in pressureinside the equipment. These additives with coagulating properties areconstituted by iron chloride, iron sulphate, ferrous sulphate, aluminiumsulphate, chloro iron sulphate, polymer flocculants, sodium silicate,sodium aluminate and strong bases, powdered lime, magnesium lime, livelime, caustic sodium hydroxide and magnesium oxide, or a mixture of atleast two of these products.

These additives, which affect the solid material, bathe in an oxidizedmedium so as to modify its macroscopic and microscopic structures.Coagulants and flocculants create the necessary electromagneticconditions to aggregate the solid hydrophobic particles in order toincrease granulation of the solid fraction. Strong bases, coagulants andflocculants occur as chemical reagents and ionic catalysts. Theseadditives produce a reaction on the organic matter and on the colloidalmaterial whereof the macroscopic structures have been broken withinstrongly aerated preceding compartments. Accelerated by favourableelectromagnetic conditions provided by the contribution of metallicions, acid-base and oxido-reduction reactions occur, with favour foroxidation and thus allow mineralisation of a part of the ionisedstructures of the organic matter and of the colloidal material. Theconsequence of increasing the hydrogen potential to very high values, 10to 12, is to destroy the aerobic micro-organisms, which might haveformed within the products.

The formation of macroscopic hydrophobic conglomerates and microscopicmineral structures also leads to reduction of the density of the solidfraction by introduction of porous lacunar vacuum.

Thanks to the intense aerobic agitating and the addition of reagents,the exchange capacity brings suitable oxygen absorption and irreversibleoxidation of positive and metallic ions working towards the desiredstability of the material.

The molecules being formed in a more or less prolonged state of anoxiaare thus transformed into their oxidised form. The ammonia NH₃ istransformed into nitrate NO₃, the hydrogen sulphide H₂S is transformedinto sulphidic acid H₂SO₃. The methane CH₄ is transformed into carbondioxide CO₂ and into water H₂O.

The method does not give off any nauseous odour. Neither does the finalproduct.

The common and heavy metals found in the product to be treated in theionised form are transformed into theirs oxides.

The products exit from the equipment by the end opposite to the inlet.The stripped gases CO₂ and NO₃ escape from the equipment along with thetreated product. The treated product is still mixed with water, themajority of which is now in the interstitial form. In this form, thewater becomes easy to extract by evaporation, draining, centrifuging orby pressing the product.

The products obtained after treating can be sold off by several avenues.In the agricultural field the product becomes a porous area of soilcapable of improving the humic clay complex of soils on the conditionthat their low content of heavy metals, copper, zinc, lead, cadmium,nickel, mercury or selenium allows this. In the field of substitutionmaterials, the product, if it originates from an initially stronglymineralised product or if it is mineralised by the method, can beintroduced in industrial manufacturing processes of brick, buildingblocks or other construction materials.

EXAMPLE

The treatment equipment comprised a steel vat measuring 10 m long and 2m in diameter, inside which were placed 2 walls cut out such that thepassage section of each cut-out formed in the wall describes a spiral,such that each wall ensures a transfer function for the sludge to betreated from one compartment to the adjacent compartment, as well as anelastic means function generating shocks and counter-currents.

This equipment was fitted with two Archimedes screws for extraction andtransfer of the sludge after treatment. The ensemble weighed 14 tonsempty.

The equipment comprised a low-pressure air compressor supplying airflowof 1000 m³/h at a pressure of 1.7 bar (absolute), and 2 systems formetering and transferring of reagents to the vat.

The whole was fed by an electrogenic group with a power of 70 kW.

Two types of reagents were used: slaked lime Ca(OH)₂ in a proportion of5% of the rate of organic matter contained in the sludge entering theequipment, and a cationic polymer in a proportion of 0.05% of the rateof dry material (organic and mineral material) contained in the sludgeentering the equipment.

The walls located inside the vat were placed perpendicularly to the flowof the sludge (and to the longitudinal axis of the vat).

They delimited three successive compartments. In the first, placed inthe direction of flow of the sludge were introduced, apart from sludge,pressurised air and the lime in an aqueous solution. The polymer in anaqueous solution was introduced into the second. Decantation of theheavy material, which was extracted by the Archimedes screws at thebottom of the vat, took place in the third. The water separated from thesolid fraction was evacuated from this third compartment, by overflow.

The sludge with a density of 1.15 entered with a rate of 407 m³/h or 450T/h. It had a rate of solid material (density 2.5) of 10% in mass of theincoming sludge, or 45 T/h or 18 m³/h.

The rate of organic material contained in this solid material was in aproportion of 10%, or 4.5 T/h; the rest of the solid material wasmineral material.

1000 m³/h of air at 1.7 bar, 225 kg/h of slaked lime and 22.5 kg/h ofpolymer were introduced.

After decantation and extraction by the Archimedes screw, sludge with adensity of 1.7 was obtained with a rate of 40 m³/h or 67 T/h. Thetreated sludge leaving the equipment contained 45 T/h or 18 m³/h ofsolid material for 22 T/hour or 22 m³/hour of water (density 1).

As it overflows from the vat, the water separated from the solidfraction of the sludge was obtained with a rate of 383 T/h or 383 m³/h.This water contained a rate of solid material of 0.02% or 77 kg/h.

1. A continuous method for treating hydrophilic sludge and slime havinga water content at least equal to or greater than 70%, comprisingallowing the sludge and slime to be decolloided, dehydrated, oxidised,ventilated, stabilised, mineralised, filtered and made porous. 2-14.(canceled).
 15. The method of claim 1, comprising the use of a stronghydraulic turbulence associated with oxidation and chemical reactionstriggered by the introduction of additives.
 16. The method of claim 1,wherein the effects of decolloidation, ventilation, mineralization andcreation of porous lacunar vacuum are partly obtained by theintroduction of coagulant additives, flocculants and strong bases.
 17. Amethod for continuous treatment of sludge having a water content atleast equal to 70%, and comprising colloidal materials, said methodcomprising the steps of: subjecting the sludge to shocks and to forcedaeration; mixing the sludge with at least one additive having coagulant,flocculant and/or basic properties; and separating the water bydecantation, filtration, draining, evaporation and/or centrifuging. 18.A method according to claim 17, wherein the sludge or slime is mixedwith an additive selected from the group consisting of iron chloride,iron sulphate, ferrous sulphate, aluminium sulphate, iron chlorosulphate, polymer flocculants, sodium silicate, sodium aluminate, strongbases, slaked lime, magnesium lime, live lime, caustic sodium hydroxide,magnesium oxide and mixtures thereof.
 19. A device for continuoustreatment of hydrophilic sludge having a water content at least equal to70%, comprising a hollow caisson traversed in a longitudinal directionby treated sludge and provided with at least one inlet for sludge to betreated and at least one outlet for the treated sludge.
 20. A deviceaccording to claim 19, comprising means for introducing pressurised airand a chemical additive into the hollow caisson at at least twophysically separated points.
 21. A device according to claim 19, whereinthe caisson comprises at least two hollow compartments interconnected topermit the transfer of products from one to the other.
 22. A deviceaccording to claim 19, further comprising means for causing mechanicalshocks and hydraulic turbulence in at least one compartment of thecaisson.
 23. A device according to claim 19, further comprising elasticmeans for causing mechanical shocks and hydraulic turbulence in at leastone compartment of the caisson.
 24. A device according to claim 19,wherein the caisson has a section transverse to the flow and a lengthparallel to the flow measuring at least 3 times the length of thelongest side of the section transverse to the flow.
 25. A deviceaccording to claim 19, wherein the caisson comprises a wall separatingtwo compartments of the caisson, the wall being holed by a flow openingof the treated products, the wall also being fitted with elastic meanscausing shocks and counter-currents.
 26. A device according to claim 19,wherein the caisson comprises a filtration device.
 27. A deviceaccording to claim 24, wherein the section transverse to the flow has asmall surface.